The present invention relates to a color image processing apparatus applicable for an image generating apparatus which copies an image of an object onto a material to which an image is to be transferred.
Color adjustment in color copier includes correction when an output image does not correctly reproduce color of an input image (original), and process for intentionally outputting color which is different from input image.
Conventionally disclosed color adjusting technique generally employs a method in which image data are converted into three attribute coordinate data representing color phase (H), lightness (L) and chroma (C) which are three attributes of color, the three attribute coordinate data are adjusted by increasing or decreasing each of the attributes on the three attribute coordinate and then, the adjusted data are returned to original color space (RGB (an additive process, i.e., the three primary colors of color light by red, green and blue) or CMY (subtractive color, i.e., the three primary colors of color material by cyan, magenta and yellow) and the like).
However, according to this method, it is known that processing time required for converting data with respect to the three attribute coordinate becomes extremely long.
For this reason, it was contrived that the RGB color space is converted into color space (such as HSV) a having high correlation with the three attribute by relatively simple computation, but precision of the correlation with the three attribute is not always sufficient.
Apart from this, in a color copier, in a color converting step utilized when input image data presented in color light three primary color (RGB) color space are converted color material three primary color (CMY) color space and reproduced on storage medium, a method in which sample color patch (color sample image) output by an apparatus (copier) itself is read, a set of RGB-CMY data of a patch of a plurality of colors is collected, and a coefficient of conversion polynomial from RGB to CMY is obtained using least squares is known as a method for obtaining parameter of color conversion.
However, according to this operation, mechanical precision is required for reading the color patch. Further, there exists contradictory conditions that it is preferable that color patch having colors as much as possible in order to obtain precise color conversion parameter, and in order to output patches of many colors on a sheet of paper having a fixed area, an area of each of patches must be small.
This fact means that precision required from reading of patches to extraction of data is severer, and when a higher priority is given to the precision, it is necessary to sufficiently increase the time for obtaining color conversion parameter. On the other hand, if the number of color patches is reduced so as to reduce the processing time, there is a problem that the precision of color conversion is lowered.
It is an object of the present invention to provide an image processing apparatus and image processing method which is applicable for a color copier and the like, and capable of adjusting and converting color at high speed, with high precision and inexpensively.
According to the present invention defined in claim 1 which is a first embodiment of the invention, there is provided a color image processing apparatus comprising: storing means for storing first image data represented in first color space corresponding to a cross point address of a color converting look-up table; color adjustment means for adjusting color in the first image data stored in the storing means to output second image data represented in the first color space so as to carry out a predetermined color adjustment in an input image; first converting means for converting the second image data output from the color adjustment means to output third image data represented in a second color space; renewal means for renewing the color converting look-up table based on the third image data output from the first converting means; and second converting means for converting fourth image data represented in a third color space which was input, based on the color converting look-up table which was renewed by the renewal means, and outputting a fifth image data represented in the second color space.
The above-described color image processing apparatus of the present invention is used in a color copier. In a conventional apparatus, after RGB/CMY conversion is carried out, color adjustment is further carried out independently. In the present invention, the parameter for RGB/CMY conversion is renewed for adjusting colors, the RGB/CMY conversion and the color adjustment are carried out at a time. With this feature, when the parameter for the RGB/CMY conversion is generated, the color adjustment has also been carried out. Therefore, it is possible to provide a color image processing apparatus capable of shorten the entire processing time.
According to claim 5 which is a second embodiment of the present invention, there is provided a color image processing apparatus comprising: storing means for storing first color coordinate data represented in first color space corresponding to a cross point address of a color converting look-up table; extracting means for extracting a first color data group from image data represented in the input first color space; basic color converting parameter generator means for generating a basic color converting parameter based on the first color data group supplied from the extracting means and a second color data group represented in a given second color space; first basic color converting means for converting basic color of the first color coordinate data stored in the storing means to output first image data represented in the second color space based on the basic color converting parameter; second color converting means for converting basic color of the first color data group extracted by the extracting means to output a third color data group represented in the second color space based on the basic color converting parameter; differential color converting parameter generator means for generating a differential color converting parameter based on the third color data group output from the second basic color converting means and a fourth color data group represented in the given second color space; differential color converting means for converting differential color of the first image data output from the first basic color converting means to output second image data represented in the second color space based on the first differential color converting parameter generated by the differential color converting parameter generator means; renewal means for renewing the color converting look-up table based on the second image data output from the differential color converting means; and second converting means for converting input image data represented in the first color space to output image data represented in the second color space.
In the above-described present invention, the look-up table for the RGB/CMY image color conversion is set, the differential color conversion is carried out in addition to the basic color conversion. With this feature, rough color conversion is set by the basic color conversion, and in a portion in the image requiring fine adjustment from a user or the like, the look-up table is finely adjusted by this differential color conversion, and it is possible to obtain a desired adjusted image. With this feature, when the parameter of the look-up table of the RGB/CMY image color converting section is made, it is possible to adjust color with high precision and at high speed without newly providing a color adjustment section.
According to the present invention defined in claim 8 which is a third embodiment of the invention, there is provided a color image processing apparatus comprising: extracting means for extracting a first color data group which is color coordinate data having a plurality of colors from input image data represented in a first color space; first generator means for generating a basic color converting parameter based on the first color data group output from the extracting means and a given second color data group; first basic color converting means for converting basic color of the input image data to output color-converted image data represented in a second color space based on the basic color converting parameter output from the generator means; second basic color converting means for converting basic color of the first color group to output a third color data group represented in the second color space based on the basic color converting parameter generated by the generator means; second generator means for generating the differential color converting parameter based on the third color data group output from the second basic color converting means and a given fourth color data group; and differential color converting means for converting differential color of the color-converted image data output from the first basic color converting means based on the differential color converting parameter output from the generator means.
In the above-described invention, both the basic color conversion and the differential color conversion are carried out at the time of the RGB/CMY image conversion of the input image like the second embodiment. The third embodiment is different from the second embodiment in that the look-up table and the color coordinate data corresponding to the cross point address are not indispensable. However, like the second embodiment, a basic color conversion is specified by the basic color conversion, and fine color conversion in accordance with fine requirements is carried out by the differential color conversion, thereby providing a color image processing apparatus which realizes a high-speed and high precision color conversion.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.